Process for the production of carboxylic acids



Patented Nov. 20, 1934 UNITED. STATES PROCESS FOR THE PRODUCTION OF CARBOXYLIC ACIDS iGilbert B. Carpenter, Bellemoor, DeL, assignor to E. I. du Pont de N emours & Company, Wil- -m1ngton, Del., a corporation of Delaware No Drawing.

Application August 24, 1931, Serial No. 559,126

5 Claims. (01. 260-116) 'This invention relates to the synthesis of organic compounds and particularly tothe preparation of higher aliphatic acids by the interaction of olefines, carbon monoxide, and steam.

pionic acid, butyric acids, etc., have been heretofore prepared by various methods. For example, propionic acid has been obtained by the reduction I of acrylic or lactic acid; by suitable Schizomycetes fermentation of the lactate or malate of calcium; or by the oxidation of propyl alcohol with dichromate solution. Such methods of preparation are necessarily expensive due principally to the relatively high cost of the raw'materials. Owing to the many important uses to which acids of this type are adaptable, many of which uses have not been exploited extensively due to their present high cost, it is obvious that a process for their preparation from raw materials, which are, at present, readily available and which will be even more readily available in the near future, will be of far-reaching importance in this art.

In my Patent No. 1,924,766, dated August 29, 1933, a process is described for the preparation of aliphatic carboxylic acids of the higher order by the reaction of steam, carbon monoxide, and an olefinic hydrocarbon, i. e. an aliphatic hydrocarbon containing a double bond,for example, the olefines ethylene, propylene, butylene, etc.,the synthesis producing from these olefines propionic, butyric, and valeric acids respectively. The acid' produced contains one more carbon atom than the unsaturated hydrocarbon treated.

An object of the present invention is to provide a process for the preparation of aliphatic carboxylic acids from steam, carbon monoxide, and olefinic hydrocarbons. invention is to provide a process for the preparation of monocarboxylic acids from steam, carbon monoxide and an olefine in the presence of a catalyst. Another object of the invention is to provide a process for, the preparation of acids having the structural formula RCHZCOOH from carbon, the R indicating a substituted or unsubstituted alkyl or aralkyl grouping. Other objects and advantages will hereinafter appear.

According to the present invention, aliphatic carboxylic acids are prepared from steam, carbon monoxide, and an olefinic hydrocarbon'by passing these materials, in the vapor phase, over a catalyst which comprises an acid salt of the iacidic oxides of elements such as, for example,

Aliphatic acids of the higher order such as pro- A further object of this I steam, carbon monoxide, and an olefinic hydrophosphorus, arsenic, tungsten, molybdenum, uranium, chromium, vanadium, boron, silicon, and zirconium. As examples of such catalysts, my invention covers such compounds as the primary and secondary phosphates of zinc, calcium, magnesium, sodium, potassium, copper, cerium, thorium, etc. and the acid salts formed between these metals and the oxides of tungsten, molybdenum, etc. These catalysts may be used alone or as admixtures and may be either unsupported or supported on the usual types of catalyst supports such as activated charcoal, fullers earth, kieselguhr, etc. I

Raw materials suitable for use in the'process are readily available from a number of sources. Thus, ethylene and. various homologues thereof are found in the gases evolved in cracking petroleum and may be separated therefrom, for example, by fractional liquefaction. It is preferable, for the sake of avoiding undesirable byproducts, that the hydrocarbon which it is desired to convert be employed in a relatively high degree of purity.

The carbon monoxide required for the synthesis may conveniently be derived from various commercial sources, such as, for example, water-gas, producer gas, etc., by liquefaction or other methods, and should likewise for the best results be relatively pure.

Inert gases, such as nitrogen, may be included with the reactants, this being advantageous in some cases from the standpoint of controlling the temperature of the exothermic reaction and of limiting the extent thereof, where it may be desired to restrict the overall conversion of the reactants for the. sake of enhancing the relative yield of the desired acids.

The relative proportions of the reactants can be varied although it has been found that very advantageous results are obtained when the steam and carbon monoxide are'in excess with respect to the olefinic hydrocarbon. Concentrations of the latter within the range of from 1 to 10% by volume of the total reactants have been employed with good results.

The use of pressures in excess of atmospheric, say from 25 to 900 atmospheres, is of advantage.

The reaction proceeds over a wide range of temperatures although the optimum temperature varies with specific'cases, depending inter alia upon the hydrocarbon being used. Generally the 1 desired reaction can be obtained at from 200 to 400 C. From the standpoint of practical operation the temperature should not be so low that the reaction rate is uneconomical nor so high as to result in undesirable by-products by decomposition and/or polymerization of raw materials. From this point of view the process has been found to operate satisfactorily at from 275 to 375 C.

The following examples will illustrate two methods of practising the invention, although the invention is not limited thereto.

Example 1.A gaseous mixture consisting of 90 parts by volume of carbon monoxide, 5 parts by volume of ethylene, and 20 parts by volume of steam is passed at a pressure of 700 atmospheres and a temperature of 350 C. over an acid zinc phosphate catalyst. This catalyst may be prepared by adding to an aqueous phosphoric acid solution a suitable amount of zinc oxide and subsequently impregnating a support, such as activated charcoal, with this solution. After drying the catalyst at approximately 120 C. it is ready for use. Upon condensation of the reaction product a condensate containing propionic acid is obtained.

Example 2.A gaseous mixture consisting of 90 parts by volume of carbon monoxide, 10 parts by volume of ethylene, and 40 parts by volume of steam, is passed at a pressure of 200 atmospheres and a temperature of 325 C. over a primary calcium phosphate catalyst. Aliphatic oarboxylic acids will be obtained including propionic acid.

The apparatus, which may be employed for conducting these reactions, may be of any conventional type and preferably one in which the temperature of exothermic reactions can be readily controlled at the desired value. Owing to the corrosive action of the acids produced, the interior of the converter and conduits leading therefrom should preferably be protected. This may be accomplished by using glass or glass-lined apparatus or by coating the inner surfaces of the apparatus with chromium or silver or using for the construction of this equipment acid-resisting alloys of, for example, molybdenum, cobalt, tungsten, chromium, manganese, or nickel.

Various changes may be made in the method hereinbefore described without departing from the invention or sacrificing the advantages thereof.

I claim:

1. In a process of reacting a gaseous mixture containing an olefinic hydrocarbon, steam, and carbon monoxide, and thereby producing an aliphatic carboxylic acid, the step which comprises passing the gaseous mixture over a catalyst containing an acid metal salt of an acidic oxide.

2. In a process of reacting a gaseous mixture containing an olefine, steam, and carbon monoxide, and thereby producing an aliphatic carboxylic acid, the step which comprises passing the gaseous mixture over a catalyst containing an acid metal salt of an acidic oxide.

3. In a process of reacting a gaseous mixture containing ethylene, steam, and carbon monoxide, and thereby producing propionic acid, the step which comprises passing the gaseous mixture over a catalyst containing an acid metal salt of an acidic oxide.

4. In a process of reacting a gaseous mixture containing ethylene, steam, and carbon monoxide, the step which comprises passing the gaseous mixture over an acid phosphate catalyst.

5. In a process of reacting a gaseous mixture containing ethylene, steam, and carbon monoxide, the step which comprises passing the gaseous mixture over a primary acid phosphate catalyst.

GILBERT B. CARPENTER. 

